Lobar collapse on chest X-ray
Lobar collapse (lobar atelectasis) is loss of air from a lobe, so that it shrinks. The usual mechanism is obstruction of the lobar bronchus, after which the trapped air is absorbed. In an adult outpatient, the cause is a central tumour until proven otherwise; in hospital patients, mucus plugging and a misplaced endotracheal tube are common. Each lobe collapses in its own direction, producing a characteristic pattern. Learning the five patterns is one of the most valuable skills in chest radiology, because collapse is easy to miss, particularly behind the heart.
1. General signs of volume loss
The collapsed lobe itself becomes denser, but the most reliable clues are the effects of lost volume on the structures around it:
- Displaced fissures: the most direct sign. The fissure moves towards the collapsing lobe.
- Hilar displacement: up for upper-lobe collapse, down for lower-lobe collapse. Remember that the right hilum should never be higher than the left.
- Elevated hemidiaphragm on the affected side.
- Tracheal and mediastinal shift towards the collapse.
- Crowding of the vessels and ribs on that side.
- Compensatory hyperinflation of the remaining lobes, which look darker with spread-out vessels.
- Silhouette sign: loss of the border that the lobe normally touches. See silhouette sign.
Air bronchograms are usually absent in obstructive collapse, because the bronchus is blocked. Their presence suggests consolidation or non-obstructive atelectasis.
2. The five lobar patterns
| Lobe | PA film | Lateral film | Pearl |
|---|---|---|---|
| Right upper | Triangular opacity at the right apex; horizontal fissure elevated and pivoting up and medially; trachea pulled right; right hilum elevated | Wedge anteriorly and superiorly; minor fissure up, major fissure forward | Golden S sign: suggests a central mass |
| Right middle | Loss of the right heart border; often subtle density; horizontal fissure depressed | Thin triangular band pointing to the hilum, between the depressed minor fissure and the forward-displaced major fissure | The least obvious on the PA. Pectus excavatum mimics it |
| Right lower | Triangular opacity at the right base, medially; loss of the medial right hemidiaphragm; right heart border preserved; right hilum depressed | Posterior triangular opacity; spine sign | Preserved heart border separates it from right middle lobe collapse |
| Left upper | Hazy veil-like opacity, densest near the hilum and fading towards the base; loss of the left heart border; aortic knob may be lost; left hilum elevated; trachea shifted left | Major fissure displaced forward; band of opacity behind the sternum | Luftsichel sign |
| Left lower | Triangular opacity behind the heart (sail sign); loss of the medial left hemidiaphragm and the descending aorta; left hilum depressed | Increased density over the lower spine (spine sign) | Very often missed. Always look behind the heart |
Sources: Radiopaedia; Radiology Masterclass; LITFL.
3. Right-sided collapses in detail
Right upper lobe
The lobe collapses upwards and medially against the mediastinum. The horizontal fissure, normally roughly horizontal at the level of the fourth anterior rib, rotates upwards. The trachea is pulled to the right and the right hilum rises.
Pearl: the Golden S sign
Normally the elevated horizontal fissure is concave from below. If a mass sits at the hilum, the medial part of the fissure bulges outwards over the mass while the lateral part remains concave, producing a reversed S shape. This Golden S sign (also called the reverse S sign) indicates a central obstructing mass. In an adult, treat it as a central bronchial carcinoma until proven otherwise and arrange CT.
Right middle lobe
The middle lobe is small and collapses into a thin wedge, so the density on the PA film can be faint. The key sign is loss of the right heart border, sometimes with a depressed horizontal fissure. The lateral view shows it clearly as a thin band pointing towards the hilum. Pectus excavatum can cause the same loss of the right heart border; look for its typical rib shape.
Right lower lobe
The lobe collapses downwards, backwards and medially. Look for a triangular opacity at the right base next to the spine, with loss of the medial part of the right hemidiaphragm. The right heart border remains visible because the lower lobe is posterior. The right interlobar artery is often lost from view as the hilum moves down. Collapse of the right middle and lower lobes together, which share the bronchus intermedius, causes loss of both the right heart border and the right hemidiaphragm.
4. Left-sided collapses in detail
Left upper lobe
The left lung has no horizontal fissure, so the left upper lobe (including the lingula) collapses forwards against the anterior chest wall. On the PA film this produces a hazy veil over the left hemithorax, densest around the hilum, through which vessels may still be seen. The left heart border is lost, the left hilum rises, and the trachea moves left. A small peak may appear on the left hemidiaphragm (a juxtaphrenic peak).
Pearl: the luftsichel sign
"Luftsichel" is German for air crescent. The superior segment of the left lower lobe over-expands and slips between the aortic arch and the collapsed upper lobe, creating a crescent of lucency alongside the aortic knob. It is a strong clue to left upper lobe collapse.
Left lower lobe
The lobe collapses down, back and medially behind the heart. On the PA film a triangular opacity overlies the heart, its lateral edge forming a straight line running down and out from the hilum: the sail sign, which can look like a double cardiac contour. The descending aorta and the medial part of the left hemidiaphragm are lost. This collapse is easily missed, especially on an under-penetrated or AP film, which is why "behind the heart" is a review area on every film.
5. Whole-lung collapse
Collapse of a whole lung gives a white hemithorax with the mediastinum and trachea shifted towards it, an elevated hemidiaphragm and crowded ribs. In ICU, first check the endotracheal tube: a tube advanced into the right main bronchus causes left lung (or right upper lobe) collapse. Mucus plugging is another common cause. In outpatients, consider an obstructing central tumour. See the white hemithorax table in pleural effusion.
6. Other types of atelectasis
- Linear (plate or discoid) atelectasis: thin horizontal bands, usually at the bases, common after surgery, with pain-limited breathing or abdominal distension. Usually harmless and transient.
- Passive (relaxation) atelectasis: lung compressed by an adjacent effusion or pneumothorax.
- Round atelectasis: a peripheral rounded opacity next to thickened pleura, with vessels curving into it like a comet tail on CT. Associated with asbestos exposure. Can mimic a tumour.
- Cicatricial atelectasis: volume loss from scarring, for example after tuberculosis, which pulls the hilum and fissures.
7. Pitfalls and mimics
- Missing left lower lobe collapse: check that the descending aorta and left hemidiaphragm are visible through the heart, and that the film is adequately penetrated.
- Calling collapse "consolidation": look for volume loss. The distinction matters because collapse may need bronchoscopy or CT.
- Right middle lobe versus right lower lobe: the right heart border is lost in middle lobe collapse and preserved in lower lobe collapse.
- Hiatus hernia behind the heart can mimic left lower lobe collapse; look for an air–fluid level.
- Pectus excavatum mimics right middle lobe collapse.
- Rotation can make a hilum look elevated or dense. Check RIPE.
- Collapse and effusion together can cancel out mediastinal shift.
Red flags: act now
Act on these
- Whole-lung collapse in a ventilated patient: check the ETT position and for mucus plugging now.
- A Golden S sign or a hilar mass with collapse: urgent CT and referral on the suspected lung cancer pathway (NICE NG12).
- New lobar collapse in an adult outpatient, or collapse that does not re-expand: needs a cause found, usually by CT and often bronchoscopy.
- Collapse after a possible inhaled foreign body, especially in a child.
What to focus on, by role
| Role | Priorities |
|---|---|
| Medical student | The general signs of volume loss, the sail sign and the right heart border rule. Practise on the lobe table. |
| Nurse | On ICU, know that collapse can follow tube displacement or secretions, and escalate a sudden fall in oxygenation. |
| Junior doctor | Check the ETT, look behind the heart, and refer collapse in an outpatient for CT. |
| Radiographer | Adequate penetration to show the retrocardiac region, and a lateral view when requested. |
| Advanced / FRCR | Golden S, luftsichel and juxtaphrenic peak signs, combined collapses, and lateral film patterns. |
References
- Radiopaedia. Lobar lung collapse. radiopaedia.org
- Radiology Masterclass. Lung collapse. radiologymasterclass.co.uk
- Life in the Fast Lane (LITFL). Golden S sign. litfl.com
- Felson B. Chest Roentgenology. Philadelphia: WB Saunders; 1973.
- NICE. Suspected cancer: recognition and referral (NG12). nice.org.uk
For education only. Not a substitute for a formal report, senior review or your local policy. Never use this page to make decisions about a real patient.